Fluid Physics

Remarkably, in spite of their relaxed state, the crew continued to enthusiastically pursue their hectic schedule of around-the-clock research in the Spacelab module. In addition to the crystal growth experiments already mentioned, a wide range of fluid physics investigations were carried out. These examined the behaviour of fluids under different influences, including the application of heat, in the hope that they could one day be used to produce high-technology glasses, ceramics, semiconductors, metals and alloys from ingredients mixed as fluids and then cooled into solids.

It was already well known that fluid motions on Earth - 'convection', caused mainly by buoyancy - often introduced defects that restricted certain materials from meeting their full potential as lenses, computer chips, turbine blades and other products. In the microgravity environment, the influence of this buoyancy-driven convection is drastically reduced and other, more subtle forces begin to have greater importance in fluid motions. The region at which a fluid interacts with another material is called its 'interface' and is particularly subject to forces causing convection in the fluid.

On 28 June, DeLucas began the Interface Configuration Experiment (ICE) inside the Glovebox. This unit very closely resembled the kind of gloveboxes used in

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ground-based research laboratories: it contained two openings, through which a crew member could insert his or her hands, and a third port through which experimental samples could be placed inside. Rugged gloves and finer surgical gloves were used, depending on the degree of precision needed when handling each sample. The Glovebox helped to reduce contamination to the Spacelab environment by keeping potentially hazardous materials in an enclosed space.

Most of the sample ampoules destined for use in the Glovebox had magnetic bases, which enabled them to 'stick', and a large plastic window in the top of the unit allowed the astronaut to view the interior. Four cameras provided still and video coverage, which could be transmitted to Earth in real-time. ''The Glovebox takes some of the rigidity out of space science,'' said Robert Naumann of the University of Alabama at Huntsville. ''It gives crew members the flexibility to adjust the experiment on-the-spot the way they would in a lab on Earth.''

After mounting video and still cameras over the Glovebox for the ICE investigation, DeLucas filled an experiment vessel with an immersion fluid composed of hydrogenated terphenyl and an aliphatic hydrocarbon. This allowed scientists to determine the behaviour of fluids in different-shaped containers in microgravity. On Earth, fluids behave in predictable ways, but it was considered important that their flows in microgravity had to be understood to better design fuel tanks and containers for biological materials or human waste.

Two other major facilities in the Spacelab module were used for fluid physics research: the Surface Tension Driven Convection Experiment (STDCE) and the Drop Physics Module (DPM). The former investigated how fluids reacted in microgravity when there were temperature differences along their interfaces. A lightweight silicone oil was used as the test fluid, because it was not susceptible to surface contamination, which could otherwise ruin such experiments. In total, almost 13 hours of video footage of the fluid were gathered from more than 38 test runs during the mission.

''Understanding this unusual phenomenon'', said STDCE Principal Investigator Simon Ostrach of Case Western University, ''is important to fundamental science. Fluid physics is the underlying science for everything that happens in microgravity research. We're building a knowledge base to help us to understand the unique laboratory environment of space.''

Three STDCE runs, each lasting eight hours, were planned, but in fact it became possible to add a fourth when an opening appeared in the crew's timeline. Typically, the experiment got underway when a command to start its computer was uplinked from the ground; one of the science crew members then powered up the experiment, inserted the heater and filled the fluid chamber with oil. When it had been determined that the oil surface was 'stable', the computer started the experimental run. The science crew could then adjust the settings or pause the experiment where necessary.

For most of the mission, Trinh supervised the bulk of the STDCE runs. The only problem was an inability of the carbon dioxide laser to reach the required power level of 3 watts in 10 of its 12 tests. Furthermore, several tiny bubbles were introduced into the test chamber during the first fill, due to a very small air gap around the heater base. Although these bubbles turned up in the experimental data, they did not adversely affect its outcome. Rather, they actually proved beneficial, because their motion - recorded on video - perfectly demonstrated the 'jitter' caused by Columbia's thruster firings.

''Our diagnosis'', said Ostrach, after watching 'live' video of the fluid on 30 June, ''had an even higher resolution than we expected. I was amazed at how clearly we could see the fluid.'' Forty-eight-hour intervals were set between each STDCE run -with three conducted on 28 and 30 June and 2 July - to enable researchers to examine and assess their data from each one and choose the most interesting phenomenon to study next. They could also see that fluid motions in both STDCE and the Solid Surface Wetting Experiment (SSWE) pulsated each time Columbia fired her thrusters.

''They correlate!'' cried backup Payload Specialist Joe Prahl in delight on 3 July, as he sat at his console at Huntsville watching a video of a 'bridge' of water between the two SSWE injectors. ''Every time the thrusters fire, the fluid wiggles! That's amazing!''

Meanwhile, in the DPM facility, containerless studies of droplet behaviour were underway. Materials processed on Earth are often constrained by containers, which can introduce their own impurities and adversely influence their properties. The DPM experiments investigated how water, glycerin and silicone oil drops and bubbles responded to certain forces, including their behaviour when dropped into immiscible (non-mixable) fluids. Using speakers mounted within the chamber, droplets were rotated, oscillated, merged, split and suspended under acoustic pressure.

It was hoped that such experiments could lead to new ways of 'encapsulating' living cells within membranes to protect them from harmful antibodies, which could lead to revolutionary drugs to cure diseases. Encapsulation studies conducted with the DPM on this mission included injections of sodium alginate droplets into a calcium chloride drop. The movement of the fluid was closely monitored by motion-picture cameras. ''We saw some things we never expected,'' said Yale University's Robert Apfel, a DPM principal investigator, after watching one run on 26 June. ''We're still flexing the facility's muscles, learning how to manipulate drops in microgravity.''

After initial concerns that the amplitude of the speakers was lower than expected, Trinh succeeded on 27 June in suspending drops of water and glycerol - a mixture 50 times more viscous than water alone - for observations of their shape and internal flow. ''It's an early study and the rotation is slowing down,'' Principal Investigator Taylor Wang - who had flown as a Payload Specialist on Spacelab-3 in April 1985 -excitedly told Trinh. ''I think we are on the right track, my friend.'' Later, Dunbar used the DPM's speakers to cause droplets to 'bounce' using soundwaves.

Still other experimental runs succeeded in contorting droplets into squares, rippled on one surface, which drew applause from ground-based scientists. ''You made my day,'' a pleased Dunbar told them. In fact, once control of the levitation speakers had been mastered by the astronauts, Trinh was able to maintain single drops for up to three hours at a time. ''We're learning a lot of new things,'' said

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Gene Trinh tends to the Drop Physics Module (DPM).

Wang. ''When the time comes to go home, we'll do the hard work - learning what our observations have to teach us. Nature will reveal its secrets to us if we are diligent enough.''

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